What is a molar pregnancy?

A molar pregnancy is a rare complication. It happens when an egg and a sperm meet at fertilisation, but the cells do not grow in a way that can support a pregnancy.

In a normal pregnancy, the fertilised egg has 23 chromosomes from the mother and 23 from the father, making a total of 46. In a molar pregnancy the wrong number of chromosomes come together, and there are abnormalities in the cells that grow to form the placenta.

There are two types of molar pregnancy:

complete molar pregnancy

partial molar pregnancy

In a complete molar pregnancy, the fertilised egg has no chromosomes from the mother and the chromosomes from the father's sperm are duplicated. This means there are two copies of chromosomes from the father. It's not possible for an embryo, amniotic sac and normal placenta to grow. Instead, the placenta forms a mass of cysts that looks like a cluster of grapes. These cysts can be seen on an ultrasound scan.

In most partial molar pregnancies, the fertilised egg has 23 chromosomes from the mother but a duplicated set from the father. This means there are a total of 69 chromosomes instead of the normal 46. This can happen when chromosomes from the sperm are copied or when two sperm fertilise the same egg.

In a partial molar pregnancy, a placenta will start to grow. This means an embryo does begin to develop. There may be a fetus, or some fetal tissue, or an amniotic sac. Unfortunately, even if there is a fetus, it simply doesn't have the right genetic make-up to survive.

Doctors sometimes describe a molar pregnancy as a hydatidiform mole. Molar pregnancy is one of a group of conditions called gestational trophoblastic tumours. Although they are called tumours, they are usually not cancerous. They may spread beyond the uterus (womb), but can be cured (Cancer Research 2009c).

After the excitement of conceiving, you're bound to feel great sadness when you find out that your pregnancy can't continue. It's also natural to feel frightened about what is happening to your body. But as long as you receive the right treatment and have good follow-up care, you're likely to make a full recovery.

How common are molar pregnancies?

Molar pregnancies are rare. BabyCenter expert Dr Patrick Chia says that in Malaysia, molar pregnancy occurs in 2.8 per 1,000 pregnancies, and it is most common in Malaysian-Chinese women, though we don't know why.

How will I know if I have a molar pregnancy?

Early on, you might have all the usual pregnancy symptoms, but at some point you'll begin to have some bleeding. However, just because you have bleeding doesn't mean you have a molar pregnancy. Bleeding in early pregnancy is fairly common, and molar pregnancies are rare. It is always worth seeing your doctor if you have any bleeding, just in case.

Bleeding caused by molar pregnancy can vary. It might be bright red or dark brown, continuous or patchy, and light or heavy. This bleeding could start as early as six weeks into your pregnancy or as late as 16 weeks.

You might also have severe nausea and vomiting (called hyperemesis), and your belly may swell up. This is because the placenta is growing fast, making your uterus expand. The fast-growing placenta pushes up your levels of the pregnancy hormone human chorionic gonadotrophin (hCG), and this is what makes you so nauseous.

A complete molar pregnancy can usually be seen on an early ultrasound scan. Your hCG levels will be much higher than in a normal pregnancy. Measuring these levels with a blood test is one way of finding out if you have a complete molar pregnancy.

It may be more difficult to find out whether you have a partial molar pregnancy, particularly if it hasn't been seen on a scan. If your pregnancy ends naturally before you have a scan, the hospital can arrange for a test to say for sure whether it was a partial molar pregnancy.

You will be asked for your permission to send samples of the miscarried tissues to a lab for analysis. This is bound to be a distressing process, but it is important to find out as much as possible. The more your doctor knows about your pregnancy, the easier it will be for her to make sure you receive the right treatment.

What's the treatment for a molar pregnancy?

If you have a molar pregnancy, you may need a minor operation called a dilatation and curettage (D&C). Your surgeon will carry out the D&C while you are asleep under a general anaesthetic.

The surgeon will widen your cervix and use gentle suction to remove the tissues from your uterus. An instrument called a curette will then be used to clear remaining molar tissues from your uterus wall.

Occasionally, not all the tissues will be removed the first time. If that's the case, you'll need a second D&C operation to remove the mole completely (Hancock and Everard 2008).

Your doctor may give you medicine to enable your body to shed the tissues by itself. You can take the medicine as tablets to swallow or as a gel or pessary to insert into your vagina.

How long will I be treated and monitored for?

It is important to monitor a molar pregnancy after it is found. This is because, if the whole molar pregnancy hasn't been removed, tiny parts can grow and spread quickly. This can still happen several months after treatment (Hancock and Everard 2008).

Occasionally, molar tissue grows into the muscle layer of the uterus. When this happens, a D&C can't get to all the molar cells to remove them. The cells can lead to what's known as persistent gestational trophoblastic disease. The disease happens in less than 15 per cent of women with complete moles, and in less than one per cent of women with partial moles (RCOG 2004, Cancer Research 2009).

Usually, the disease shows as an invasive mole. An invasive mole can develop after a partial molar pregnancy, but it's more likely to happen after a complete molar pregnancy. The most common symptom of an invasive mole is irregular or continued bleeding, even after a D&C.

If you have an invasive mole, you'll need drug treatment (chemotherapy). The drugs kill off any remaining molar cells. With prompt treatment, nearly 100 per cent of cases of invasive moles in the uterus are curable.

It's important to make sure all the molar cells have gone from the uterus wall. This is because the cells can spread via the blood to other organs, including the lungs, liver and brain. You may have further testing, to be sure that the disease hasn't gone beyond your uterus. Although molar cells can spread, they are not cancerous and this condition has a cure rate of nearly 100 per cent.

In a very few cases, however, persistent gestational trophoblastic disease can lead to an extremely rare form of cancer. This is called choriocarcinoma, and spreads to other organs. This can also be successfully treated with chemotherapy (ISSTD 2010). To give you an idea of how rare it is, the condition occurs in one in 30,000 of all pregnancies, including normal pregnancies and miscarriages.

Once you're in complete remission, you'll need to have your hCG levels monitored on and off for the rest of your life.

When can I try to get pregnant again?

The good news is that, in the vast majority of cases, having a molar pregnancy doesn't affect your chances of having a normal pregnancy next time. But it is important to wait until your doctor says you can start trying again.

If you haven't had chemotherapy, you'll need to wait up to six months after your hCG levels go back to normal before trying to get pregnant again (RCOG 2004). If you have had chemotherapy, you are usually recommended to wait 12 months before trying.

If you become pregnant before these times, you have a greater chance of having another molar pregnancy. Your doctor won't be able to tell whether your rising hCG levels are because of your pregnancy or because abnormal tissue is growing back.

You should use contraception until it is safe for you to try for a baby. It's best to use condoms. The pill is not recommended, because if you take it when your hCG levels are still high, it can make you more likely to need chemotherapy. Coils (IUDs) are not suitable either, until your hCG levels and your periods return to normal (Cancer Research 2009, RCOG 2004).

Your odds of having another molar pregnancy are small, about one or two per cent (RCOG 2004). When you're pregnant again, you'll have an ultrasound scan in your first trimester to make sure all is well.

How can I cope with my sense of fear and loss?

Having a molar pregnancy can be frightening and upsetting. Like any woman who has miscarried, you're having to deal with the loss of your pregnancy. As well as this, you've had an unusual condition that you may not have heard of before. It may seem to take forever before you have the all clear and it's only natural to feel anxious about your own health.

You may be fearful about getting pregnant again. Rest assured that you're very unlikely to have another molar pregnancy. There's also no need to worry if you've had chemotherapy. It won't affect your next pregnancy at all.

Your husband may feel sad at the loss of your pregnancy, or find it difficult to support you. Keep talking and try to share your grief together. If either of you is finding it hard to cope with your feelings you could talk to your doctor .

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